Add per-account folder customization page (#855)

Introduce a dedicated settings page that lets users reorder, hide,
and pin/unpin folders per account. Folders are organized into Pinned,
Categories (Gmail only), and More sections with drag-to-reorder via
ListView. New Order column on MailItemFolder persists the custom
layout; the default sort falls back to alphabetic when no custom
order is set. A reset action wipes all customization in a single
transaction and restores system-folder stickiness.

Co-authored-by: Claude <noreply@anthropic.com>

Wino.Mail.ViewModels/Data/FolderCustomizationItemViewModel.cs

@@ -0,0 +1,26 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using Wino.Core.Domain.Entities.Mail;
+
+namespace Wino.Mail.ViewModels.Data;
+
+/// <summary>
+/// Per-folder row shown on the Folder Customization page. Wraps the underlying
+/// <see cref="MailItemFolder"/> entity and exposes observable flags for binding.
+/// </summary>
+public partial class FolderCustomizationItemViewModel : ObservableObject
+{
+    public MailItemFolder Folder { get; }
+
+    [ObservableProperty]
+    public partial bool IsHidden { get; set; }
+
+    public string FolderName => Folder.FolderName;
+    public bool IsSystemFolder => Folder.IsSystemFolder;
+    public Core.Domain.Enums.SpecialFolderType SpecialFolderType => Folder.SpecialFolderType;
+
+    public FolderCustomizationItemViewModel(MailItemFolder folder)
+    {
+        Folder = folder;
+        IsHidden = folder.IsHidden;
+    }
+}